Another thought, you may already know this, on the fridge, most newer units require 12V control voltage no matter what system you are running it on. So the TC has to be plugged in or on battery for it to operate on gas or 120V.
If you are familiar with 120V electrical, you can bypass the control circuit to test it with 120V only by making a 120V cord that will plug onto the 120V heating element. It should be below freeze when left overnight. You would still have to test it with the control circuit and gas which requires 12V.
Be careful, it is 120V power.